1. Field of the Invention
The present invention relates to an exhaust control apparatus which can cancel an exhaust gas flow amount difference between cylinder groups of an internal combustion engine, and an exhaust gas flow rate estimating method which can be used therefor.
2. Description of the Related Art
As an internal combustion engine having a structure in which cylinder groups are connected to different exhaust passages, there has been, for example, known a V-type engine in which a cylinder group is structured in each of banks and each of the cylinder groups is connected to the different exhaust passage. Further, as an exhaust control apparatus applied to this kind of V-type engine, there has been known an exhaust control apparatus which controls an ignition timing of each bank such that each of catalysts reaches a temperature suitable for reproduction by canceling a dispersion in temperature between the catalysts at the time of reproducing both catalysts in the exhaust passages with respect to a sulfur poisoning (refer to JP 11-117786 A). Further, as the prior art documents in connection with the present invention, JPH06-213044 A and JPH07-174048 A exist additionally.
In the V-type engine as mentioned above, a dispersion is generated in the exhaust gas flow amount introduced to each of the exhaust passages due to a difference in volume charging efficiency between the cylinder groups, a difference in flow amount characteristic of an EGR apparatus and the like, and some kind or another disadvantages maybe generated owing to the matter. For example, since a speed of deterioration of an exhaust purifying catalyst due to the sulfur poisoning or the like correlates with the exhaust gas flow amount, the speed of deterioration is different in the exhaust passage if the exhaust gas flow amount is different in each of the exhaust passages. In this case, an optimum reproduction timing of the exhaust purifying catalyst is displaced between the cylinder groups, there are problems that a reproducing process is executed later than the optimum reproduction timing, whereby a recovery of an exhaust purifying performance is delayed, or the reproducing process is executed earlier than the optimum reproduction timing, whereby unnecessary energy is consumed.